1. Field of the Invention
The present invention relates to a pressure reducing valve and in particular to a pressure reducing valve with a grease-free (lubricant-free) guide mechanism for guiding an opening/closing valve.
2. Description of the Prior Art
In conventional pressure reducing valves, a guide mechanism is often used to improve the sealing performance in a main valve and in a relief valve (air release valve) thereof. Although conventional seal-packing-type pressure reducing valves are equipped with a guide mechanism for the relief valve, the resistance imposed on movements of the relief valve due to a seal packing is great because a guiding component of the guide mechanism needs to be equipped with a sealing mechanism. Conventional diaphragm-type pressure reducing valves are higher in sensitivity than seal-packing-type pressure reducing valves. In a diaphragm-type pressure reducing valve with no guide mechanism for the relief valve, the resistance caused upon actuation of the pressure reducing valve is small, however the relief valve becomes freely movable so that sealing repeatability is poor upon a return of the relief valve after it is opened, and accordingly, and hence the sealing performance is poor. In addition, the sealing performance deteriorates by a positional deviation of a diaphragm assembly upon installation thereof, which is a fairly common occurring problem.
A pressure reducing valve in which a valve shaft is formed as a separate element from a valve body so that a valve port can be securely sealed by the valve body even if the valve shaft tilts or is decentered is also known in the art (Japanese Unexamined Patent Publication Nos. H05-113828, H05-257540 and H11-119837
However, this conventional type pressure reducing valve needs to be lubricated with lubricating oil such as grease because a sliding portion, in which metals are in sliding contact with each other, exists in the guide mechanism of the valve body and also in the valve shaft. Therefore, in the case where the pressure reducing valve is used in an environment such as a clean room which does not tolerate impurities, the lubricating oil may get scattered.